The present invention relates in general to a system and method for actively damping boom noise within an enclosure and, more particularly, to such a system and method which employs both a motion sensor and a collocated microphone and speaker noise control scheme within an enclosure, such as an automobile cabin.
When driven, the cabins of large automobiles, such as sport utility vehicles and minivans, exhibit a relatively high level of low-frequency “impact boom” noise, particularly when driven over rough road surfaces. The low-frequency road noise generated within an automobile cabin is a result of vibro-acoustic resonance within the cabin interior and is commonly characterized by a number of low-frequency resonant modes. This can detrimentally affect occupant comfort and well being, as well as the quality of voice and music within the enclosure. The structural dynamics of the panels which form the cabin, and the acoustic dynamics of the enclosure therein, make up the elements of this vibro-acoustic system.
Known in the relevant art is the use of passive noise control materials in the interiors of large automobiles. While plush interiors, thick carpets, and other sound absorbing materials are effective in abating higher frequency sound, they become increasingly less effective at lower frequencies and totally ineffective at bass frequencies. Frequently, the overuse of such treatments results in a “dead” sounding cabin with a loss of the natural clarity and sparkle of voice and music. Consequently, an active noise control system is required.
The general principals of active noise control are well established and basically consist of detecting the noise to be controlled, and replaying the detected noise in antiphase via a loudspeaker so that the regenerated noise destructively interferes with the source noise. While several conventional techniques have been found to effectively absorb the energy of offending, low-frequency modes which cause boominess within an enclosure, none are without significant shortcomings. The objectionably large size of conventional low-frequency absorbers, such as Helmholtz resonators (HR), as well as their inability to be tuned to multiple frequencies, and thus requiring a bank of HRs to be installed, make the use of such conventional absorbers in automobile cabins and other relatively small enclosures highly impractical. Other known active noise control systems control noise in only limited local areas within a three-dimensional space.
U.S. Pat. No. 5,974,155 teaches a system and method for actively dampening low-frequency noise within an enclosure wherein an electronic feedback loop is employed to drive an acoustic dampening source within an enclosure. The system further employs an acoustic wave sensor or microphone for detecting the low-frequency noise to be dampened. However, in addition to the acoustic resonance generated by low-frequency road noise, a vehicle can also exhibit adjacent vibro-acoustic resonance originating from the structural vibration of the panels which form the vehicle cabin. The active acoustic dampening system of the '155 patent was designed to abate cabin originated resonance. Consequently, the need remains in the relevant art for an active acoustic dampening system which effectively dampens acoustic resonance originating from both the cabin, as well as the vibro-acoustic resonance caused by panel vibration in an automobile.
While further known is the use of detection means which record the rotational velocity of a motor, as well as those which employ an accelerometer or motion sensor, the art is devoid of a system which employs the combination of a collocated microphone and speaker arrangement with that of a motion sensor-based, low-frequency noise control scheme within an enclosure.
Accordingly, the need remains in the present art for a system and method that effectively reduces low-frequency noise within an enclosure, in particular, the enclosure of an automobile where the noise generated within the cabin is characterized by a number of low-frequency vibro-acoustic modes of significant magnitude.